Currently, assessment of speech sound disorders in bilingual children is inadequate because of lack of knowledge on typical and atypical bilingual speech development. As a result, bilingual children are often over- and under-identified for speech sound disorders. To address the need for normative data, the proposed study explores typical bilingual speech development in Spanish-English 3-year olds. Single word samples from 120 typically-developing children, 30 each from four language groups, will be compared. Language groups, determined by parent and teacher surveys, are 1) monolingual English (EN, from English- speaking homes in English-speaking classrooms), 2) monolingual Spanish (SP, from Spanish-speaking homes in Spanish-speaking classrooms), 3) simultaneous (SM), and 4) sequential (SQ) Spanish-English bilinguals. SM are from Spanish-English and SQ are from Spanish home environments. Data will be collected at the beginning (3;3-3;9) and end (3;9-4;3) of the children's Head Start year. Speech productions will be compared in English between EN, SP, and SQ, and in Spanish between SP, SM, and SQ. Analyses of phonetic transcription of speech samples will include phonetic & phonotactic inventory, phoneme accuracy, and phonological error patterns, compared by language groups. The PI will compare fall and spring samples cross-sectionally, and change over time within groups from fall to spring. A subset of the English samples will be analyzed acoustically, comparing vowel F1, F2-F1, and duration differences in front tense/lax vowel pairs produced in (C)CVC word shapes. It is hypothesized that bilingual children will have similar phonetic inventories but will make greater errors in their speech compared to SP in Spanish and EN in English. Bilingual children are also expected to have greater variability in vowel acoustic measures. Between bilinguals, SQ are predicted to make more errors than SM in English but fewer than SM in Spanish, because of their more recent English exposure. SQ are predicted to be more accurate than SM in Spanish in the fall, although SQ are expected to decrease in Spanish vowel accuracy from fall to spring, due to introduction of English to their developing phonology. From results, the PI will develop a preliminary understanding of articulatory and phonological contributions to bilingual speech development, provide a baseline for research on speech development in other language environments and in bilingual disorders. [unreadable] [unreadable] [unreadable]